Tumor necrosis factor-alpha (“TNFα), alternatively referred to as “cachexin” or “cachectin,” is a 185 amino acid-long cytokine that is released by damaged white blood cells, endothelium cells and certain tissues. TNFα is formed in vivo by the cleavage of a 212 amino acid-long precursor transmembrane protein. Upon cleavage of this precursor transmembrane protein, soluble molecules are released that aggregate to form complexes. These complexes then bind to tumor necrosis factor receptors (TNF-R) found on a variety of cells to thereby result in an array of pro-inflammatory effects, such as the release of the pro-inflammatory cytokines interleukin-6 and interleukin-8, the enhancement of endothelial layer permeability (thereby allowing for leukocyte migration), the activation of neutrophils and eosinophils, and the induction of tissue-degrading enzymes produced by synoviocytes and chondrocytes.
Elevated levels of TNFα are associated with many disease states. For example, increased concentrations of TNFα are often found in the joints of individuals suffering from rheumatoid arthritis. In these patients, the induction of tissue-degrading enzymes by TNFα causes degradation and erosion of joint and bone tissues. In addition to rheumatoid arthritis, Crohn's disease is another disease associated with increased concentrations of TNFα. While the exact cause of Crohn's disease is unknown, patients suffering from Crohn's disease experience inflammation and ulceration of the digestive tract. Other diseases and conditions that have been linked to increased levels of TNFα include psoriatic arthritis, ulcerative colitis, plaque psoriasis, sarcoidosis, ankylosis spondylitis, and cytokine-induced islet destruction in autoimmune diabetes.
Current approaches for treating individuals suffering from rheumatoid arthritis (as well as other diseases associated with increased TNFα) include neutralizing or otherwise diminishing the ability of TNFα to bind to TNFα receptors in the body. In one such approach, patients are administered monoclonal antibodies that bind to TNFα (i.e., anti-TNFα-antibodies), thereby inhibiting TNFα's ability to bind to TNFα receptors. Commercially available forms of anti-TNFα-antibodies are available, including, infliximab (marketed under the REMICADE® name, Centocor, Inc., Malvern, Pa.) and adalimumab (marketed under the HUMIRA™ name, Abbott Laboratories, Abbott Park, Ill.). Infliximab is typically administered over at least two hours via an intravenous infusion while adalimumab is typically administered subcutaneously every two weeks. Because infliximab is a chimeric antibody, there is concern that administration of this antibody to humans can result in an immunogenic reaction. Further, even though adalimumab is a human monoclonal antibody specific for TNF, approximately 5% of adult rheumatoid arthritis patients developed low-titer antibodies to adalimumab at least once during treatment (as demonstrated over three studies) and the long term immunogenicity of adalimumab is unknown.
Another approach for neutralizing or diminishing the effects of TNFα includes binding circulating TNFα, thereby reducing the amount of TNFα available for binding to functioning cell surface receptors. This approach can be effected by administering TNFα receptors (or TNFα-like receptors). By administering an excess of exogenous TNFα receptors (or TNFα-like receptors), circulating TNFα is bound to the exogenous and non-functioning receptors resulting in significantly decreased amounts of TNFα available for activating endogenous TNFα receptors. Commercially available pharmaceutical formulations that are based on this approach include etanercept (marketed under the ENBREL®, Immuunex Corporation, Thousand Oaks, Calif.), a p75 type II TNF soluble receptor. Although not currently available commercially, PEGsunercept (or PEG-sTNF-RI) is a PEGylated version of a p55 type I TNF receptor. It has been alleged that etanercept has been associated with rare cases of central nervous system disorders such as multiple sclerosis, myelitis and optic neuritis and pancytopenia, including aplastic anemia. There is relatively little experience with PEGsunercept to know whether it will suffer from the same concerns as etanercept.
Thus, there remains a need to address, for example, the immunogenicity concerns associated with therapies intended to decrease the effects TNFα in vivo. The present invention is intended to address the immunogencity concerns (and/or other concerns) by, for example, attaching a water-soluble polymer to an anti-TNF antibody, thereby forming a conjugate between the water-soluble polymer and the anti-TNF antibody. The present invention includes this and other embodiments, which are believed to be new and completely unsuggested by the art.